Radio Frequency Identification (RFID) systems represent the next step in automatic identification techniques started by the familiar bar code schemes. Whereas bar code systems require line-of-sight (LOS) contact between a scanner and the bar code being identified, RFID techniques do not require LOS contact. This is a critical distinction because bar code systems often need manual intervention to ensure LOS contact between a bar code label and the bar code scanner. In sharp contrast, RFID systems eliminate the need for manual alignment between an RFID tag and an RFID reader or interrogator, thereby keeping labor costs at a minimum. In addition, bar code labels can become soiled in transit, rendering them unreadable. Because RFID tags are read using RF transmissions instead of optical transmissions, such soiling need not render RFID tags unreadable. Moreover, RFID tags may be written to in write-once or write-many fashions whereas once a bar code label has been printed further modifications are impossible. These advantages of RFID systems have resulted in the rapid growth of this technology despite the higher costs of RFID tags as compared to a printed bar code label.
Although RFID systems offer certain advantages over a traditional bar code schemes their use is also not without concerns. One such concern is radiations, such as electric signal, emitted by RFID tags when made operational. Generally, in a RFID system, an RFID tag includes a transponder and a tag antenna, and communicates with an RFID transceiver pursuant to the receipt of a signal, such as interrogation or encoding signal, from the RFID transceiver. The signal causes the RFID transponder to emit via the tag antenna a signal, such as an identification or encoding verification signal, that is received by the RFID transceiver. In passive RFID systems, the RFID tag has no power source of its own and therefore the interrogation signal from the RFID transceiver also provides operating power to the RFID tag.
A concern in the foregoing approach is when numerous RFID tags are within range of each other while a signal is transmitted from a transceiver to one of the RFID tags, and which becomes particularly acute during the initial encoding of the RFID tags, where an often large number of RFID tags are juxtaposed in an assembly line fashion during manufacturing. In this setting, the encoding signal from a transceiver to an intended recipient transponder can cause the intended transponder to generate electric fields, such as dipole field, which in turn would excite the tag antenna in the intended RFID tag to transmit encoding and operating radiations to adjacent RFID tags. The adjacent RFID tags will then in turn become operational and encoded with the information intended for the recipient transponder, thus detrimentally overwriting the adjacent tags previous encoding. This results in one or more adjacent RFID tags having the same identification information as the intended RFID tag, and thus become distinguishable from each other during future use. In addition, the information encoded on the intended recipient transponder will also be overwritten in the same manner once the transceiver begins encoding of the next adjacent RFID tag.
As the size of the RFID tags continue to decrease due to technological advancement in the field, the number of adjacent RFID tags that are within range of the intended RFID tag in an assembly line increases, thus further exacerbating the above-described problem. In addition, the operating power required to encode RFID tags is also decreasing, such as down to 10 micro-Watts from 110 micro-Watts, thus making each RFID tag more susceptible to operating radiations received from adjacent RFID tags and thus becoming encoded with information intended for an adjacent RFID tag.
Accordingly, there is a need in the art for nullifying the unwanted operating radiations transmitted from an intended RFID tag to adjacent RFID tags.